The present invention relates to a bottom outlet or discharge for metallurgical vessels receiving smelted steel, particularly tundishes, wherein a sleeve brick has inserted therein a nozzle brick, and wherein there is provided a heat insulating layer covering the sleeve brick and at least the area of the discharge.
Metallurgical vessels to receive steel melts, particularly such as tundishes, have a fire-resistant lining of bricks connected with mortar and a fire-resistant substance. In the bottom of the vessel, the bottom outlet or discharge is formed by a sleeve brick and a nozzle brick of wear-resistant material inserted within the sleeve brick. When it becomes necessary to replace a used nozzle brick, it is generally also then necessary to replace the sleeve brick, and thus a reformed fire-resistant substance is primarily used between the brick work of the lining and the sleeve brick. German Gebrauchsmuster 76 19 744 discloses a heat-insulating lining provided on top of the permanent fire-resistant lining in a decanting vessel for liquid metal, whereby a reduced preheating or the elimination of preheating, a better protection of the permanent lining and the possibility of convenient cleaning of the vessel are achieved. Further, the heat-insulating lining can cover the sleeve brick at the discharge and can extend to the nozzle brick. This is done in order to obtain the advantage that the durability of the sleeve brick is increased and so that the sleeve brick can be fitted directly to the fire-resistant brickwork without using therebetween a fire-resistant substance.
However, in practice, it has been found, when employing such a bottom outlet or discharge in metallurgical vessels, that during operation not only the nozzle brick but also the sleeve brick which is protected by the heat insulating layer is highly stressed, and that after wear of the nozzle brick sufficient to require replacement thereof, it is also necessary to replace the sleeve brick since it has been destroyed due to the formation of cracks. It has specifically been found that safe operation of the metallurgical vessel cannot be achieved, for example, with a nozzle brick formed on the basis of zirconium silicate, and particularly of zirconium oxide, and a sleeve brick on the basis of calcined bauxite with clay bonding.